Many piping system applications in chemical and natural resource recovery industries involve the handling of corrosive, erosive, scaling or otherwise harsh aqueous fluids. One economic approach to handling these difficult fluids is to spin cast a fluid-resistant liner onto the interior surface of a low cost, non-fluid-resistant pipe. The pipe material, such as low carbon steel, provides structural support for the costlier and/or structurally inadequate liner. One type of fluid-resistant liner contains an inorganic cementitious material, such as a Portland-like cement.
Common lining material precursors contain a variety of inorganic fillers and cementing agents, and form a hydraulic slurry when mixed with water. The hydraulic slurry, which can temporarily flow like a liquid, is applied to the interior surface of the pipe and allowed to cure (slowly hydrate or precipitate) into a rigid pipe liner. Some hydraulic (water-based) cements (e.g., Portland cement), and liners made therefrom, are subject to chemical (e.g., corrosion) and mechanical (e.g., erosive) attack by certain harsh aqueous fluids, such as geothermal brines.
The primary objectives when creating new material components which can be used to fabricate a protective pipe liner are that the components: 1) produce a workable slurry which can be applied to the pipe interior; 2) harden into a liner which desirably attaches to and moves with the pipe; 3) resist long term fluid chemical and mechanical attack; and 4) provide an effective barrier to chemical attack of the underlying piping. The lined pipe should also be rugged, safe, reliable, environmentally acceptable, and cost effective.
A common problem with current concrete liner compositions is their propensity to crack. Geothermal applications can subject the liners to severe conditions resulting from differential thermal expansion (including that induced by thermal shock), vibration, and fluid flow. These conditions tend to crack brittle materials or liners, particularly those experiencing tensile stresses. Many such materials are noted to shrink upon setting or curing. Such shrinkage increases the tensile stress within the liner; thus, cracking may even occur during preparation. Cracks in the liner allow chemical attack of the underlying steel pipe. An expansive or non-shrinking cement may be employed as a lining material to maintain size and/or to generate compressive stress within the material in order to offset or circumvent shrinkage. Often such cements may not compact well.
Additives are being sought to improve the compactibility of the solid slurry components, hence densifying the resulting lining material, and to reduce shrinkage, thereby increasing the materials resistance to cracking.